An air introducing device as described above is disclosed in German Patent Publication (DE) 3,643,175. The known device comprises a distribution space having air outlet openings formed by holes in an apertured bottom of the distribution space. These outlet openings lead into a chamber arranged below the distribution space. The chamber has a bottom with air nozzles functioning as outlet openings. The on-center spacing between the air nozzles is at least three times the nozzle exit diameter but may be as large as twelve times the exit diameter. The individual air jets produceable by the known device are not completely free of air turbulences, however, the produced air jets make it possible to generate a stable displacement flow having a relatively small displacement flow.
Thus, the known device has the substantial disadvantage that it is not suitable for producing a sufficiently stable, low turbulence displacement flow in rooms or enclosed spaces having high ceilings. Sheds or halls used for coating aircrafts with outer protective skins, such as lacquer skins, require the introduction of fresh air at substantial heights. The air inlets for introducing the fresh air are located in the shed ceiling which may be as high as 20 to 25 meters. Used air is sucked out through air outlets in the floor leading into air exhaust channels in the floor for the exhaust of the used air. Thus, the air flow in such sheds is vertically downwardly from the ceiling to the floor. For keeping such sheds sufficiently ventilated it is necessary to remove solvent vapors, lacquer aerosols, and the like, with an air flow that is as low as possible in turbulence so that these air contaminants are displaced on a direct path toward the air exhaust channels. Therefore, the fresh air flow must be low in turbulence. A low turbulence air flow is also necessary for avoiding or at least minimizing an all too extensive intermixing of these contaminants with the air in the shed. Additionally, the time during which the contaminants are present, should also be as short as possible, because high concentrations of lacquer aerosols and solvents in the breathing air adversely affect the health of personnel present in such facilities and the quality of the surfaces that are to be lacquer coated.
The lacquer coating operation is followed by a drying of the sprayed-on lacquer. The spraying is performed at a temperature within the range of about 20.degree. to 22.degree. C., whereby the fresh air is blown in isothermally more or less or slightly under-cooled. However, the drying is performed while the temperature of the fresh air inflow is increased to accelerate the drying process. Thus, the fresh air inflow has a temperature higher than the room temperature. The same operating conditions also prevail already during the lacquer spraying operation when the outdoor temperature is lower than the temperature in the shed so that heat losses by heat transmission must be covered by heat introduced with the fresh air.
Thus, for achieving a stable displacement flow it is necessary that the jet impulse is variable in response to the difference in the room temperature of the shed and the fresh air temperature. In case heating is required, the fresh air temperature is higher than the room temperature. Therefore the air exit impulse of the fresh air jets must be higher than in the cooling case at which time the room temperature is higher than the fresh air being introduced into the shed.
Furthermore, it is necessary to adapt the jet impulse of the fresh air to the particular type of aircraft that is to be coated. This is so, because aircraft with a larger body height are exposed to the fresh air flow more intensely than aircraft having a smaller body height. This is primarily due to the fact that the air blowout plane of the fresh air inlets is located closer to a tall aircraft body than to a smaller aircraft body.